Personally I would suggest you to use a BKF recovery tool to repair corrupt BKF file.
First try to repair your file with demo version of the software. The demo version of the software allows you to preview the content of the file prior to recovery and if you see the content of corrupted file in preview then it means that your file has been repaired. You need to purchase the software to save the repaired file.
I'd recommend getting in touch with a vendor of a repair tool, such as SysTools.
BKF files are most commonly used with Windows file back ups. If the file is somehow corrupted, you might want to consider investing in software that will allow you to repair the format of the file.
There are plenty of BKF repair tools out there, so shop around!
The one made by SysTools is just one example. If Microsoft have their own product, that might be more reliable - but I can't find evidence of a Microsoft BKF file recover program...
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